Specific cells of the C. elegans hypodamis fuse during embryonic morphogenesis. We would like to use the techniques of transmission electron microscope and scanning electron microscopy to examine the way in which membranes fuse during formation of the hypodermal syncytium. Embryos will be accurately staged to the developmental period at which fusions occur. This will be accomplished using the 4-D microscopy system developed at the IMR. These embryos will then be frozen using high-pressure freezing. Specimens will be freeze substituted in acetone, brought to room temperature, embedded and sectioned. We will then examine thin serial sections via TEM or thick sections by de-embedding and examination in the HRSEM.